U.S. patent application number 10/804148 was filed with the patent office on 2004-09-23 for measuring system for recording angular and linear absolute values.
Invention is credited to Rodi, Anton.
Application Number | 20040183002 10/804148 |
Document ID | / |
Family ID | 32797962 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040183002 |
Kind Code |
A1 |
Rodi, Anton |
September 23, 2004 |
Measuring system for recording angular and linear absolute
values
Abstract
An absolute measuring system for the determination of angles or
paths is described. During normal operation the encoder of this
system is fed by a voltage supply (mains). If the voltage supply
fails the encoder is switched to an auxiliary power supply which
uses less energy. In this operating mode the encoder only
calculates a coarse value of the measured value which it stores in
the memory. To maintain the auxiliary power supply a chargeable
memory is provided which is assigned to the encoder.
Inventors: |
Rodi, Anton; (Leimen,
DE) |
Correspondence
Address: |
LERNER AND GREENBERG, P.A.
POST OFFICE BOX 2480
HOLLYWOOD
FL
33022-2480
US
|
Family ID: |
32797962 |
Appl. No.: |
10/804148 |
Filed: |
March 17, 2004 |
Current U.S.
Class: |
250/231.14 |
Current CPC
Class: |
E05Y 2800/252 20130101;
E05Y 2400/612 20130101; G01D 5/2492 20130101 |
Class at
Publication: |
250/231.14 |
International
Class: |
G01D 005/34 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2003 |
DE |
103 12 045.9 |
Claims
What is claimed is
1) an absolute measuring system (1, 12) for the determination of
angles or paths, whose encoder (1) is fed during normal operation
by a voltage supply (mains) (14, 19), where the encoder (1) may be
switched to an auxiliary power supply which uses less energy when
the voltage supply (14, 19) fails, and where there is only a coarse
determination of the measured value made during this mode of
operation, in particular according to patent . . . (patent
application 103 120 45.9), characterized in that a chargeable
memory (2) is provided and assigned to the encoder (1) to maintain
the auxiliary power supply.
2) A measuring system as recited in claim 1, characterized in that
the memory is a battery (2).
3) A measuring system as recited in claim 1, characterized in that
the memory is a chargeable condenser.
4) A measuring system as recited in claim 1, characterized in that
the memory is a chargeable battery and a chargeable condenser.
5) A measuring system as recited in claim 1, characterized in that
the memory is a chargeable condenser and a non chargeable
battery.
6) A measuring system as recited in one of the claims 1 to 5,
characterized in that the chargeable memory (2) is arranged at
least in the vicinity of the encoder (1).
7) A measuring system as recited in claim 6, characterized in that
the memory is located in the encoder (1).
8) A measuring system as recited in claim 6, characterized in that
the memory (18) is located in the encoder side of a connector
(10).
9) A measuring system as recited in one of the claims 1 to 8,
characterized in that the memory (2,18) is charged by solar
cells.
10) A measuring system as recited in one of the claims 1 to 8,
characterized in that the memory (2, 18) is charged by means of
electromagnetic waves.
11) A measuring system as recited in one of the claims 1 to 8,
characterized in that the memory (2, 18) is charged by means of
transformer coupling.
12) A measuring system as recited in one of the claims 1 to 8,
characterized in that the memory (2, 18) is charged by means of
motion induced field induction.
13) A measuring system as recited in one of the claims 1 to 8,
characterized in that the memory (2, 18) is charged by the mains
(14) and/or an external auxiliary power supply (13) via cables
(9).
14) A measuring system as recited in claim 13, characterized in
that the cables (9) are fiber optic cables at least on the side
close to the encoder.
15) A measuring system as recited in one of the claims 1 to 14,
characterized in that the signals are transferred between the
encoder (1) and a system control (12) via radio waves by means of a
transmitter/receiver (31, 33).
16) A measuring system as recited in claim 15, characterized in
that there is a reduced radio transmission (20, 21) in battery
operation when the voltage supply (19) fails.
Description
[0001] The angle and linear measuring systems currently used in
industry are predominantly those which record the relative
displacement of the measuring unit incrementally as well as add to
a previously determined or inputted reference value depending on
direction and thus calculate the relevant absolute value. The
disadvantage of this is that the absolute position is lost when the
mains is switched off or fails and requires a new reference to be
determined or inputted. These measuring systems are also very
sensitive to disturbance variables and transient malfunctions and
are hence unsafe.
[0002] This problem has been somewhat alleviated in the case of
linear measuring systems by applying a more or less expensive and
defined reference track to the scale which simplified the travel of
the reference and allowed limited control of the measured
values.
[0003] For angle measuring systems or rotary encoders the reference
impulse for the travel of the reference has been taken for each
revolution and used to determine the initial absolute value which
can also be checked and corrected. Other measures must be taken in
the case of multitum encoders, however, if the revolutions
themselves i.e. multiples of 360.degree.=2.pi. need to be recorded.
Either a separate drive is integrated into the measuring system to
record its position using position sensors for recording all of the
revolutions made separately, or a battery is used that allows a
separate integrated rotational measuring system with energy saving
sensors and counting logic to be supplied with power and
permanently stores information during mains failure. The drives are
bulky, limit durability as well as the rotational positions that
can be recorded and are also costly due to the additional sensor
technology. The separate rotational measuring system, equipped
mainly with permanent magnets and counting logic by means of
magnetically conductible segment disks as well as Reed contacts, is
also bulky and has limited durability due to its mechanical
contacts as well as critical battery life in places prone to
excessive temperature where long life industrial encoders are
integrated e.g. electric motors. For angle measuring systems there
have also been repeated attempts to avoid using a drive or battery
by designing devices using permanent magnets and coils in such a
way that the switching energy resulting from the changing magnetic
field was used to count the rotational position and store the
counter reading. More detailed information about this can be found
for example in patent specification no. (to be supplied). But these
measuring devices are also bulky and have limited durability due to
their use of special electronic Flash-memory components which also
means that they are not very widespread.
[0004] Reacting to the increasing desire for absolute measuring
systems, which at least save on the travel of a reference and
provide safe recording of measured values that are as free from
interference as possible and make them available for data transfer,
new absolute measuring systems have been developed and brought onto
the market in recent years. For Instance, patent specification DE
19505176A1 describes an optical process that uses an
m-sequence-code arranged in a line. However, a PCR code located on
a separate track has also been used for magnetic linear measuring
systems. Apart from the problem that the code length must be
determined for each scale length, magnetic scales are bulky
(approx. 20 mm wide.times.2 mm high) and expensive to manufacture.
The dimensions of the encoders are also dependant on the code
length and magnetic pole pitch, e.g. 11 Bit.times.5 mm.gtoreq.55 mm
long and vary in their sensor arrangements which also depends on
the code length and have different evaluation electronics for the
different code sequences.
[0005] An additional difficulty for angle measuring systems is that
the code selection with a beginning and end must be continuously
selected in cycles and the code length as well as code pitch must
be adjusted to the diameter of the scale. This permits just one
system with a fixed diameter and means a new design of encoder is
always required if the diameter is changed. In addition there is
still no satisfactory solution to the problem of recording multiple
revolutions which is becoming increasingly important, for example,
in the field of robotics.
[0006] The object forming the basis of the invention is to provide
solutions to the above-mentioned shortcomings and a lasting
solution for angle and linear absolute measuring systems of the
future. This is achieved by the features of claim 1.
[0007] It is preferable in this respect to refer to a novel method
of creating absolute values for angles and paths according to
patent right application 103 120 45.9, in which only the sensor
arrangement needs to be supplied with power to record segments when
mains power fails. This is done according to the present invention
by using a chargeable, stored auxiliary power supply belonging to
the measuring device: the object of the main application can be
more clearly stated as being a measuring system to record absolute
values of angles and paths in which these are recorded by a sensor
arrangement and the scale is composed of at least two segments
designed to record absolute values in the same way. In this system
the scale has at least one track to determine the absolute value of
the particular segment reached by means of the sensor arrangement
and circuits which provide the total absolute value from the
absolute value of the segment and the calculated absolute value
within the segment for further processing. The system is powered by
the mains. There is also a switch arrangement provided which
switches to an auxiliary power supply when the mains power fails.
In this operating mode the sensor arrangement is only used to
determine the absolute value of the particular segment reached. In
principle the invention may be used for all absolute measuring
systems that record at least the absolute encoded segments with a
sensor and its accompanying switch arrangement in a way which saves
energy when the mains power fails.
[0008] The absolute measuring systems designed according to the
above mentioned patent right application may be very small and
suitable for Integrating Into actuators (electric motors;
mechanical, electrical, pneumatic and hydraulic controlling
elements) as well as apparatus and machines. The increasing
miniaturization of semiconductors will enable the complete absolute
measuring system including the sensor to be fitted into the size of
a single chip in the foreseeable future. The location of the
chargeable and stored auxiliary power supply will be increasingly
away from the immediate vicinity of the integrated measuring
device, which is an advantage if for no other reason than because
of the lack of space for integration at the place of measurement
and the adverse environmental conditions such as extremes of
temperature which are often found there.
[0009] In any event the chargeable auxiliary power supply belonging
to the measuring device should always be located before the first
interface e.g. connector in the mains cabling to the superior
control device. This will ensure that when the external mains
connection to the control device is broken there is no loss of
stored measured data. It is beneficial to locate the chargeable
auxiliary power supply in the housing of the first pluggable
interface.
[0010] Of course it is beneficial to locate the chargeable
auxiliary power supply in the housing of the measuring system
itself if space and environmental conditions allow. It is also
appropriate for a number of reasons to integrate the chargeable
auxiliary power supply in a special housing immediately next to the
limited space where the absolute measuring system is integrated and
connect it to the measuring system with the shortest possible
connectors. Most importantly, if there is no wired external mains
power supply, a separate housing for the chargeable auxiliary power
supply may contain additional arrangements that can use wireless
external power to assist in charging the auxiliary power supply.
This may use for instance the energy from electromagnetic radiation
for close and long range or also by means of transformer coupling
of alternating currents or by a displacement current of mutually
inducing electric and magnetic fields. Light rays such as sunlight
are also a form of electromagnetic waves for energy transfer as are
for example light rays which may be with a frequency visible or
invisible to humans. All physical principles of conversion which
can be considered as practicable methods of electrically charging
the auxiliary power supply may be used to charge the auxiliary
power supply. This should include in particular conversion of
kinetic energy into electrical charge that can be obtained from the
relative motion of an encoder and a scale with alternating magnetic
poles by an induction effect with at least one coil system. A large
number of physical methods for wireless charging of the auxiliary
power supply are possible according to how they can be integrated
as well as the environmental conditions and can enable counting of
segments due to the low energy consumption of the selected sensor
arrangement. An example is the possible use of well-known solar
cell or even radio energy converters to maintain sufficient charge
in the design of the measuring system according to the
invention.
[0011] Maintaining sufficient charge in the auxiliary power supply
of the measuring system is very helpful for keeping the selected
charge capacity as small as possible. This basic storing of charge
of the auxiliary power supply is crucial to the size/volume of the
energy carrier, but also for how long the reserve supply will last
when it is not possible to maintain sufficient charging. The most
important thing here is that the transferable energy E=u *i*t=P*t
is sufficient to allow as much energy as is required for use in the
measuring system. A useful life of approx. 10 years gives an
indication for choosing what size to make the auxiliary power
supply which employs for example a rechargeable battery. Supposing
the recharging energy makes up x % of the total energy requirement,
the charge capacity of the auxiliary power carrier is
therefore:
Q=(1-x)*i*t;
[0012] where i represents the current of the measuring device and t
its period of use.
[0013] For x 0 50% and
[0014] i=10 pA
[0015] t=365 days/year*24 h/day*10 years
[0016] t=87.6*10.sup.3 h
[0017] Q=(1-x)*i*t=0.5* 10-5A*87.6*10.sup.3h
[0018] Q=43.8*10-2*A*h=438 mAh
[0019] The charge capacity allows the use of for example coin cell
batteries, which are small and can be fitted inside the housing of,
say, a connector. The essential thing here is to design the sensor
arrangement with the lowest possible current requirement and to
base the energy for recharging the auxiliary power supply/battery
as far as possible on the required power output. By doing this, the
dimensions and charge capacity will be kept small and have the
right size for emergency use.
[0020] The chargeable auxiliary power supply may be designed in a
number of ways, those of practicable use being strongly influenced
by cost and conditions of use and safety. The following are
examples of designs that can be used:
[0021] rechargeable battery
[0022] chargeable condenser
[0023] chargeable condenser with rechargeable battery
[0024] chargeable condenser with non chargeable battery
[0025] The rechargeable battery will be the most common and
preferred version for standard angle and linear measuring systems
especially where there is a wired mains power supply. This
arrangement is of particular benefit when there is a need for an
additional external auxiliary power supply. This redundant
arrangement provides for "single fault safety" and allows the
mutual exchange/repair of the auxiliary power supply of the
measuring system and the external auxiliary power supply during
power cuts.
[0026] The chargeable condenser as sole auxiliary power supply can
be considered cost-effective when possible interruptions to the
mains supply are only less than approx. 1 hour but also on those
occasions when the loss of the absolute position just for short
interruptions is not acceptable and referencing of the measuring
device can be carried out straight away during longer power
failures.
[0027] The rechargeable battery with chargeable condenser is
beneficial when there is no external auxiliary power supply
present. The arrangement is redundant during a fault and allows the
battery to be exchanged if necessary, without loss of measured
data. In addition the battery can be made smaller depending on the
condenser.
[0028] The chargeable condenser in combination with a non
chargeable battery is an alternative worth mentioning, in order to
save cost. This version is particularly useful if a longer
interruption of the mains supply would only be expected in
exceptional circumstances.
[0029] If there is an additional external auxiliary power supply
located in the control system away from the absolute measuring
system, the chargeable auxiliary power supply belonging to the
measuring system can be made particularly small. The chargeable
auxiliary power supply belonging to the measuring system should be
constructed for use only in cases where there is a normal
short-term disconnection of the external auxiliary power supply
from the measuring system, e.g. when removing a connector or
repairs/exchanges during servicing.
[0030] In the case of the redundant combination of the external
auxiliary power supply with the chargeable auxiliary power supply
belonging to the measuring system it is appropriate to use a
rechargeable small battery or the chargeable condenser if only
short-term disconnection from the external auxiliary power supply
is to be expected. However, attention must always be paid to the
low current drain of the measuring system during interruptions in
mains power in the design of such systems as well, since the
external auxiliary power supply has a limited charge capacity and
is used for a large number of sensors as well as other controls for
data backup, e.g. for multiaxle robots.
[0031] The rechargeable auxiliary power supply belonging to the
absolute measuring system offers the additional advantage of radio
transmission of measured data suitable for use in industry. This
not only reduces the expense of costly cables and connectors for
transmitting measured data but also saves the considerable cost
involved in bus systems for distributed control systems. It also
solves or considerably reduces the problem of expensive cabling and
damage caused to it by changes in conditions for moving absolute
encoders. Even if a wireless auxiliary power supply is
insufficient, for example where there is an intensive exchange of
measured data, the only additional cabling required is for the
mains power supply. This consists of just two power cables since
even an external auxiliary power supply which might be present can
feed the absolute encoder via these cables. These two cables can be
fitted in the controls to the absolute encoders as bus connections
without any special shielding. Not only are the thin cables
flexible and space saving for fitting into instruments and
machines, their sensitivity to changing conditions is considerably
reduced and have the advantage that costs for cabling and
connectors are reduced.
[0032] In the following, embodiments and the further development of
the invention will be described in more detail with reference to
the drawings.
[0033] It shows:
[0034] FIG. 1 an embodiment with the chargeable auxiliary power
supply in the encoder
[0035] FIG. 2 an embodiment with an external auxiliary power
supply
[0036] FIG. 3 an embodiment with signal transfer by radio
[0037] FIG. 4 an embodiment without connecting cables between the
encoder and system control
[0038] In FIG. 1 an absolute encoder is labelled 1. It has a
rechargeable auxiliary power supply e.g. a rechargeable battery 2.
Logic 3 is used to record the segments. The sensor arrangements for
both absolute values are labelled 4. Block 5 contains the logic for
measured signal processing and transfer. The moving scale via whose
tracks both measured values are determined is labelled 6. The
measured results transferred from the encoder 1 are fed via the
serial data exchange 17 on the control side of control electronics
16 to the evaluation unit and measured value processing.
[0039] In 7 the measured data are transferred via cables 8 to a
system control 12 where they are converted accordingly. The encoder
1 is supplied with power via cables 9. A connector 10/11 is fitted
to the transfer lines 8,9.
[0040] The system control 12 is provided with a mains supply 14,
which supplies the encoder via the mains cable 15 and the transfer
lines 9. This also charges the battery 2.
[0041] When mains power fails the auxiliary power supply 13 present
can take over the supply to the encoder 1. If this also fails or
connector 10/11 is removed the encoder 1 still remains active but
only with respect to determining the segments. This energy saving
operation can be ensured for a long period of time due to the
supply by the auxiliary power supply 2 adjusted accordingly.
Switching to this emergency power is activated by a comparator
5a.
[0042] The embodiment shown in FIG. 2 differs from that of FIG. 1
in that the chargeable auxiliary power supply 2 of FIG. 1 is
arranged as a chargeable auxiliary power supply 18 outside the
encoder 1 and in fact in the connector component 10 close to the
encoder. This is charged by a charging device 19 attached to or
integrated into the connector. The remaining components are
labelled in the same way as in FIG. 1. When mains power fails, the
auxiliary power supply is fed via the left half of cable 9 and
cable 2' to the encoder 1 to give it limited operation. In this
case there is no provision for an external auxiliary power supply
as with 14 in FIG. 1. The charging device 19 derives its power from
one of the above-mentioned options. Cables 8 for data transfer may
also be fiber optic cables at least between connector component 10
and encoder 1.
[0043] In the embodiment shown in FIG. 3 the auxiliary power supply
2 is again housed in the encoder. The mains supply 14 and if
necessary external auxiliary power supply 13 supply the encoder 1
and its chargeable auxiliary power supply 2 via cables 9, to which
a connector 22/23 is fitted. In this case data transfer is by
radio, which is why the encoder 1 and system control 12 are each
equipped with a send and receive antenna 20 or 21 and a transmitter
and receiver 30 or 31. In this case cables 9 may also be fiber
optic cables, especially on the encoder side.
[0044] In the embodiment of FIG. 4 there is no longer a cable
connection between the encoder 1 and the system control 12. In this
case, there is a transmitter and receiver 33 with a send and
receive antenna 20 outside but close to the encoder 1. The send and
receive data of logic 5 are transferred to the send and receive
data converter via another logic 32 and the serial measured data
exchange 7 to logic 5 or from this via radio (transmitter/receiver
31,33) to the system control 12 (especially SSI). Once again the
chargeable auxiliary power supply 18 is located outside the encoder
1 as in FIG. 2. Similarly it is charged by a charging device 19
which is also supplied by the mains. Reduced radio transmission
during battery operation is also feasible here.
* * * * *